Method of manufacturing bronze colors



Oct. 17, 1933. E KRAMER 1,930,684

METHOD OF MANUFACTURING BRONZE COLORS Filed Sept. 29, 1930 L IH F A Q I.2 86 1 I 3% In N \o N m r! INVENTOR. a n ERWIN KEHMEH- I *1 BY 2 a ATTORNE Y.

Patented Oct. 17, 1933 UNITED STATES mn'rnon or MANUFACTURING nnonzr:

conoas Erwin Kramer, Berlin, Germany, assignor to Hartstofl-MetallAktiengesellschaft tag), Berlin-Collenick, Germany (Hame- ApplicationSeptember 29, 1930, Serial No. 485,284, and in Germany September 30,1929 2 Claims.

My invention relates to a method of manufacturing bronze colors with theaid of devices "or apparatus or machines designed similar to, andoperating like, ball-mills, except that in this particular manner by thesuitable dimensioning of balls and their effect of falling and by thechoosing of a suitable radius of curvature of the balls small metalparts, as, for instance, foil waste, pulverulent metal, little thinpieces of wire and the like, are expanded or flattened. Transforming therespective metallic pieces or particles into pulverulent state ispreferably carried out similar to the process disclosed in German PatentNo. 410,514, but when that process is adapted to bronze certaindifficulties are encountered; these difficulties are eliminated by thepresent invention.

It is old, in connection with the pounding of bronze, to add an oil or afat to the respective metal in order to prevent the particles to adhereto'the wall of the pounding vat, as well as to get welded together bythe heat. While, however, the amount of oil or fat can be easilyregulated where pounding vats or troughs are used in view of thecomparatively small dimensions of these receptacles, matters are quiteotherwise if a large number of steel balls must be used, that is to say,where such balls are the operating members or tools, especially if theballs are to act in drums of a long axial length. The difiiculties metwith are still greater if the expanding or flattening operation is to becarried out continually or uninterruptedly, viz in that the metalparticles enter the drum at one end and the pulverulent metal leaves thedrum at its other end.

Because of the metal particles being expanded or flattened the originaloil or fat film with which they were provided becomes ever thinner, andsimultaneously therewith the particles move from one end of the drum tothe other end. While, thus, the amount of the oil or fat iscomparatively great at the inlet end of the drum, it decreasesconsiderably on the way of the particles to the other end of the drum,and if the film becomes very thin then arises the danger that the metalparticles adhere to the balls whereby the operating surface of theselatter becomes irregular and the expanding or flattening procedure is nolonger carried out in the desired and necessary manner. On the contrary,the metal particles which are already very thin are ground down to sucha degree that the bronze finally obtained is practically useless.Besides, also the surface of the steel balls is affected and destroyedso much that they become unsuited for further use, and instead ofexpanding and flattening the metal particles grind them into pulverulentstate.

On the other hand, a too large amount of fat into bronze, but if thatmaterial is foil waste which is torn to pieces and must be furthersubdivided.

Now, the present invention aims at reducing the time of the passage ofthe metal particles through the drum, or, in other words, the timeduring which no further fat or oil is supplied to the material in thedrum. That purpose can be attained in two different ways, the oneconsisting in reducing the length of the drum and the other in blowingmore powerfully through the drum. It is, however, also possible tocombine these two means with one another.

The treated material leaving the drum is conducted to a sifting devicein which from the finished particles are separated those that are notyet in a finished state. These latter particles are returned to the drumso as to be treated a second time, and when being re-introduced they aresupplied with an additional amount of oil or fat, either directly or bytheir contact with the fresh particles which carry sufiiciently much oilwith them, since do also the balls.

Shortening the length of the drum means also a reduction of themanufacturing costs thereof, and, furthermore, a smaller space isrequired to house it. Besides, the entire arrangement and combination ofparts can be smaller and also a correspondingly lesser number of steelballs is required, and since also the amount of the metal particles, i.e. the more or less reduced metal in the drum, is smaller, the danger ofan explosion is reduced. The smaller supply of the drum with the metalto be treated involves the further advantage that the machine when incontinual operation reaches more quickly a stable uniform operationwhich is favorable to the quality of the product which is more uniformor, more precisely speaking, highly uniform. The reduction in the timeduring which this state is attained is also important if now one metaland then another metal is to be treated and converted into bronze, themore so because prior to the working of the other metal, the first mustbe completely removed from the machine, i. e. from the drum.

Making use of a current of air of such a strength that not only thefinished particles are carried out of the drum, but also largerparticles is advantageous also in another respect. The separation of thefine and the coarse particles is connected with certain difliculties. Itmust be borne in mind that the sectional area which is available in thedrum for the air passing through it is limited, as the dimensions of thedrum, especially its diameter, must be determined or chosen from acommercial point of view, and furthermore, the fine particles tend toadhere to the coarse ones whereby the separation is rendered even moredifilcult. While in grinding other substances in ball mills it isgenerally desired to attain a very fine grain it is otherwise withbronze because attention must be paid to the particles beingandremaining fiat or foil-like, since otherwise their light-refractingcapacity ceases which is that particular property by which bronze isdistinguished. Particles that have become too small impair the goodappearance of the product and render it more or less dark or even black,and it is hardly or not at all pomble to remove such particlesafterwards by sifting, as their fineness is already by far too small,considerably below the finest sieve having 10000 meshes to the squarecentimeter. The too small particles possess furthermore the disagreeableproperty of grinding down the brone foils whereby the product may berendered practically useless. 7

With the known grinding process in a ball mill the mutual grinding downof the individual particles plays, a very important part. If, however,the grinding in the ball-mill is carried out according to the presentimproved method, the manner of operation of the mill is materiallychanged in that the metal particles are -so worked that they areconverted into foils, but this working procedure must be continued onlyto a certain extent, viz until the desired product has been attained,because otherwise, if the drum containing the balls continues to actupon the material the latter is turned into a poorly looking powderofbrown or grey color. Interrupting the procedure is the more'difiicult, the finer the bronze is to be. At any rate, care must betaken that that operation of the mill by and during which the metalparticles are transformed into bronze changes to that other operation atwhich the material is merely ground in the ordinary manner.

Now, the object in view is attained, according to this invention, by theutilizing of the current of air conducted through the mill in aparticular manner. While in the old method of operating ball mills inconnection with a current of air the chief object is to attain apossibly fine powder and the blast serves solely the purpose of carryingthe powder out of the mill, but is of no infiuence upon thesize or shapeof the particles, the blast, in the present improved method, is used toprevent the production of too fine a powder or, in other words, toprevent carrying the disintegration too far, and to remove finishedparticles prior to their being destroyed. Thus, the form of theindividual particles of the material can be acted on by means of theblast.

In any event, there is this difficulty as regards the removal of thefinished particles at the proper time, that many thereof are held fastby and between the balls or are held down by the continually fallingballs. It is, therefore, necessary to make the blast considerablystronger than would be sufilcient to carry away the finished particles,and it is a part of this invention to carry away also particles that aremore or less unfinished and to separate them from the other ones in aseparate apparatus especially designed for this purpose. An importantpart of this apparatus is a sifter which can be ad- Justed just to thedesired sifting fineness withi,oao,ee4

out any change oflthe strength of the blast. With the usual or ordinaryslfters,-the velocity of the blast can be diminished by means of athrottle-fiap or the like, but, of course, the velocity is then reducednot solely in thesifter but in the entire circuit of the blast, and thusalso in the flattening drum. The sectional area of the sifter is ofcourse made larger than the sectional area of the drum so that the speedof the blast in the sifter is lower than in the drum, and certain of theparticles which the blast carries away can drop. The resistance of thesifter to the blast is comparatively low, and according to thisinvention that resistance is still more reduced in order to attain astill greater sifting fineness, and that reduction is effected byincreasing the sectional area of the sifter. This means, of course, areduction of the speed of the blast, so that the finer particles canfall down.

That larger sectional area cannot entail a slow-- er flow of the blastthrough the drum, but it may be that the fiow is accelerated. But sincethe resistance which the sifter presents to the blast is very slight, ashas already been mentioned, the variation of the sectional area of thesifter is practically of no influence upon the fiow of the blast in andthrough the drum. That speed-which'has been found as being the mostfavorable for the purpose in view is substantially maintained.

Because of the employment of steel balls with short radius havingmathematically only points at which they contact with one another andbetween which only minute amounts of the small metal particles can bepresent or retained, the possibility is presented to produceparticularly thin and, therefore, particularly valuable bronze, and theparticular manner of sifting permits to remove the respective particlesfrom the drum just when they are in the proper condition or state,before they are destroyed.

Anyhow, the finer the bronze, the greater is the danger of explosion,especially if aluminium bronze is being made, and it has, therefore,already been proposed to fill the drum with an indifferent gas, forinstance hydrogen, in order to remove oxygen completely from theapparatus. But, nevertheless, fine aluminium bronze, irrespective ofwhether it is in an atmosphere of air or of hydrogen, possesses theproperty to decompose automatically when it comes in contact with freshair. This behaviour is due to the fact that the fine powder has taken upa large amount of the gas and has retained it by absorption. It is thena mere matter of chance whether the powder explodes or not. This is atonce comprehensible in the presence of oxygen in the powder, but, infact, also hydrogen is not able to serve as a protective in the air.Just as platinum sponge commences to glow in the open air when a currentof hydrogen is conducted onto it, so the same phenomena take place whenthe finely distributed or subdivided aluminium is saturated withhydrogen.

It is obviously very important to keep the gases 1 parts of theapparatus through which the bronze has to pass are kept filled with agas or gas mixture containing neither oxygen, nor hydrogen, also noilluminating gas, but such gases as nitrogen, carbonic acid and heliummay be used.

Also anhydrous gases. as combustion gases, can

be employed. The metal particles are, as it were, provided with aprotective skin by which the danger of the particles igniting at theopen air is very considerably reduced, nearly to zero.

In order to-carry the method into practice I prefer to make use of theapparatus shown diagrammatically and by way of example on theaccompanying drawing in which Figure 1 is chiefly a verticallongitudinal section through, and partly a side-view of, an apparatusdesigned according to this invention, and Figure 2 is a transversesection in the plane A-B of Fig. 1.

The metal particles to be flattened which are in pulverulent state arecontained in a receptacle 1 from which they are conveyed through a tube3 by means of a screw conveyor 2. 4 is an oiling device for supplyingsaid pulverulent metal particles with oil which drops down upon themwhile they pass through the tube 3. The oiled particles are conveyed bythe conveyor to the tubes and tubular members 5, 9 and 10, and throughthis latter member they pass into the rotatory drum 12 which containsthe steel balls 15. The ends of the drum are conical and these conicalends are separated from the cylindrical main part of the drum by coarsesieves 13 and 14 that permit the pulverulent particles to enter into thedrum but retain the balls therein. The steel balls are the means ormembers by which the flattening of the metal particles is effected.

The drum is rotated by any suitable means. I have abstained from showingsuch means as they are known in the art and do not form a part of thisinvention. The blast is produced by means of a blower 16. The air isforced through tubes 17 and 30, from which latter it is conducted intothe passage 29 and further through the tubular member 10 into the drum.Those particles of the powder which the blast can carry away are carriedby it through the sieve 13 into the drum where they are acted on by thesteel balls, and thereafter the treated, i. e. flattened particles arefurther carried by the blast through the sieve 14 into the tube 18 andthrough this into the top member 19 of the sifter. The body 20 of thisis quadrangular in transverse section and in it are provided superposedoblique sheet-metal plates 21, the uppermost of which is the first thatreceives the powder. From this plate the powder falls successivelyoverall other ones, that is to say, only upon the lowermost portionsthereof, through the oblique passages 24 in the direction indicated bythe arrows 23, and while thus being conducted, it is subjected to theaction of the blast so that those particles which are in the propercondition are carried upwards through between the plates 21. There areshown as an example four such passages, viz 34, 35, 36 and 37, and theyall terminate in a passage 25 through which the product passes into aso-called cyclone 26 or into an equivalent apparatus in whichthe bronzeparticles and the blast are separated from one another. The finishedbronze falls down into a vessel 27, or an equivalent member. The airleaves the cyclone through the pipe 28 by which it is returned to theblower 16. Those metal particles that have fallen down into thelowermost part of the sifter body are conveyed into the tubular member29 by means of a rotary blade-valve 31 that is driven in the suitablemanner by any suitable means.

Instead of the oil receptacle 4, any other suitable oiling device may beused. The oil may be stearin oil or the like. Another such or similaroiling device 6 isprovided at an enlarged portion '7 of the pipe 5, anda third device for the purpose in view is the oiling device 8 which isprovided upon the top of the tubular member 30. It is, thus, possible tooil either only the fresh material introduced into the apparatus fromthe receptacle 1, or also the particles that have left the sifterthrough the members 31 and 29, the oil being in this case introducedinto the blast streaming through the pipes 17 and 30. The kind of thefat or oil and the amount used in the several oilers depend upon thekind of the metal and upon the shape of the metal particles. It ispossible to use only one oiling place; that must be ascertained bytests. It is, at any rate, favorable for the result or the success ofthe procedure to supply oil to those particles that have already madetheir way through the drum and the sifter and are returned to the drumin order to pass a second time through the circuit.

One may diminish the sectional area of the sifter, that is to say, ofits body portion 20, by means of the flaps 32 and 33, of which the fiap32 is shown in closed position and the other in open position. When theflap 32 is closed, as in Fig. 1, the passage 37 does no longer form aportion of the circuit, and when the flap 33 is closed, also the passage36 does no longer form a portion of that circuit. The free sectionalarea can, thus, be varied accordirg to requirements, and the fineness ofthe product determined at will. This is always without any detrimentalinfluence upon the drum, in that the sectional area of the drum remainsunchanged, as does also the velocity of the blast on its flowtherethrough.

As the circuit forms a closed path, it can be filled with an indifferentgas, as has already been stated.

If necessary or desirable, a hose filter, or a plurality of suchfilters, may be inserted between the pipe 28 and the cyclone 26 in orderto free the blast completely from the metal dust. Finally, it is alsopossible to provide a plurality of sifting devices adapted to subdividethe bronze still more as to the fineness of the particles and to providefor this purpose a corresponding plurality of such receiving receptaclesas 2'? or equivalents therefor.

I claim:

1. In the method of producing bronze colors in the shape of very thinmetal foils in ball mills, in which through the ball containing drumthere is conducted a gaseous current capable of carrying away from thedrum the finished foils as well as materially larger unfinished metalparticles and in which from the finished foils the unfinished metalparticles are separated and returned to the drum, the step of supplyingto the separated unfinishedmetal particles at the inlet end of the druman additional amount of lubricant through contact with a fresh supply oflubricated particles.

2. The method as specified in claim 1, wherein the drum.

E'RWIN KRAMER.

